This invention relates to improving the properties of film forming vinyl polymers. These polymers have many uses particularly in coating and impregnation applications and are most useful as dispersions in water. Making water-based coatings or impregnants with polymers having low Tg values enables the aqueous-based paint to be applied at normal room temperatures without the use of a plasticizer but results in films which in many cases are inadequately hard and tough after drying, at least for some applications. In many cases, however, it is desirable to achieve the hardness, block resistance, solvent resistance, and print resistance of a hard film. To accomplish this a polymer with a glass transition temperature (Tg) above about 30.degree. C. is required and such polymers require a coalescent or fugitive plasticizer to yield coherent films at ambient temperature or below.
Conventional coalescents such as butyl CELLOSOLVE.RTM., butyl CARBITOL.RTM., TEXANOL.RTM., and the like are useful to facilitate film formation from hard polymers (Tg substantially above room temperature) and even from soft polymers (Tg less than room temperature) when film formation is required at temperatures lower than normal room temperature. However, after film formation is complete the coalescent evaporates at a rate depending on its boiling point and may generate odor and pollution problems.
The composition of this invention overcomes these disadvantages by incorporating a "reactive coalescent" which, as defined herein, after it has facilitated film formation, does not substantially evaporate but reacts to become part of the film.